Date of Award

2026-05-01

Degree Name

Doctor of Philosophy

Department

Metallurgical And Materials Engineering

Advisor(s)

David A. Roberson

Abstract

This dissertation studies the structure-processing-function relationships of additively manufactured shape memory polymer blends, with emphasis on mechanical anisotropy. Chemical exposure, thermally activated recovery, self-healing behavior, and 4D printed functional response. Two polyester-based blends were studied: a binary blend composed of polycaprolactone and thermoplastic polyurethane (PCL/TPU) blend, and a ternary blend composed of polycaprolactone/thermoplastic polyurethane/ polylactic acid (PCL/TPU/PLA) blend. The materials were melt-compounded using a twin-extruder to produce filament for fused filament fabrication (FFF). Specimens were fabricated using four different raster orientations, 0°,90°, 0/90°, and 45°, to investigate the influence of processing architecture and composition on the mechanical performance, recovery behavior, and multifunctional response of the polymer blends. To assess environmental durability and recovery capability, specimens were exposed to ethyl acetate and acetic acid for seven days. The effects of the chemical exposure were analyzed through tensile testing, dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), swelling behavior, and scanning electron microscopy (SEM). Both blend systems exhibited strong raster orientation-dependent behavior in terms of mechanical performance and chemical susceptibility. Solvent exposure promoted interfacial degradation and delamination along raster boundaries, mainly in specimens printed at 45° raster orientations. The ternary PCL/TPU/PLA blend exhibits greater stiffness and strength dependent raster orientation behavior, and solvent-induced degradation was also perceived due to increased phase heterogeneity. FTIR- ATR and swelling analyses exposed that ethyl acetate primarily induced reversible plasticization, while acetic acid exposure caused irreversible hydrolysis and polymer bond degradation. Thermal annealing at the shape memory transition temperature supported partial recovery of mechanical properties through thermally activated chain mobility and stress relaxation mechanisms. Furthermore, statistical analysis confirmed that several annealed specimens recovered tensile properties to values comparable to those of untreated control specimens. Moreover, to evaluate recovery behavior, the shape memory and 4D printing response of the materials were investigated using spatially varying lattice structures programmed through thermomechanical cycling, activated using Digital Image Correlation (DIC), and analyzed through angle- versus-time measurements for PCL/TPU and PCL/TPU/PLA systems. In addition to this, a comparison of the blend systems to PLA, the blend systems demonstrate slower but more controlled recovery behavior, indicating that polymer composition and complex geometry can be used to temporally actuate response for applications involving adaptive structures and soft robotic systems.

Language

en

Provenance

Received from ProQuest

File Size

113 p.

File Format

application/pdf

Rights Holder

Katia Lizbeth Delgado Ramos

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